The present invention relates to a method and apparatus for maintaining quality control in a friction welding operation, particularly inertial welding operations for which a simplified version of the present invention is especially adapted.
The invention also relates, possibly in a more specific way, to computerized apparatus which substantially instantaneously provides a signal indicating whether one or more operating conditions are within predetermined limits indicating an acceptable bond formed at the interface of the workpieces. In association with a friction welding machine including control means for automatically repeating a friction welding operation, the computerized apparatus may be employed to terminate operation of the machine if an operating condition is outside of acceptable limits during a welding operation.
A brief review of different types of friction welding is set forth below in order to more accurately define the present invention. Two types of friction welding are commonly referred to as conventional friction welding and inertial welding.
In a conventional friction welding operation, one workpiece is rotated against another workpiece at a relatively constant speed and under a relatively constant axial load until the interface between the workpieces is heated to a plastic condition. Relative rotation between the workpieces is then rapidly stopped. The axial load may then be increased to improve the strength of the bond at the interface.
Inertial welding refers to a process wherein energy for accomplishing a bond between two workpieces is provided by a rotating inertial mass. The inertial mass is accelerated to a selected speed to store a predetermined amount of energy. The workpieces are then pressed together by an axial load while inertial energy stored in the rotating mass is consumed at the interface to produce frictional heating and plastic working of the interface. The rotational speed of the inertial mass continuously decreases and the entire energy of the inertial mass is preferably consumed at the interface of the workpieces. However, in certain applications, only a selected portion of the energy in the inertial mass is consumed at the interface.
The present invention is particularly concerned with the specific operation described above. For example, the type of bond accomplished by inertial welding may be simulated as illustrated in one instance by U.S. Pat. No. 3,542,274, issued on Nov. 24, 1972 and assigned to the assignee of the present invention. That patent refers to a speed-programmed friction welder wherein the relative speed of rotation between two workpieces is closely controlled by electronic means.
A comparison of the speed-programmed weld cycle of the above-noted patent with an inertial welding operation indicates that both operations are generally characterized by the relative speed of rotation between the workpieces being varied in a substantially predetermined manner from an initial, relatively high speed with low torque at the interface to a relatively low speed with high torque at the interface, a bond being substantially completed between the workpieces at their interface as relative rotation ceases.